Glucosinolate Content of Potential Brassicaceae Biofumigant Crops

Glucosinolates, sulfur containing thioglucosides occurring in aliphatic, aromatic, and indoles forms, are defensive compounds found primarily in the Brassicaceae (mustard) family. In damaged tissue, myrosinase degrades glucosinolates into isothiocyanates, nitriles, epithionitriles, and thiocyanates.  The predominant breakdown products, isothiocyanates, are generated from aliphatic glucosinolates. Isothiocyanates remain active in soil up to a few weeks, and are general biocides.  Green manure crops in the Brassicaceae family have been used as biofumigants but the effectiveness of specific accessions depend on the specific glucosinolates profile and concentrations.  Our objective was to determine levels of aliphatic, aromatic, and indole glucosinolates in a wide range of Brassicaceae potential biofumigants. We evaluated accessions from Brassica barrelieri (1 accession), B. juncea (10 accessions), B. napus (6 accessions), B. nigra (3 accessions), B. oxyrrhina (1 accession), B. rapa (4 accessions), Camelina sativa (2 accessions), Enarthrocarpus arcuatus (1 accession), E. sativa (1 accession), Sinapis alba (3 accessions), S. arvensis (1 accession), and S. flexuosa (1 accession).  The seed were obtained from commercial sources and the USDA Mustard Germplasm Repository in Ames, IA.   The accessions were seeded in 10 cm pots filled with greenhouse media. The experiment was a randomized complete block design with four replications. The mustards were thinned to two plants per pot and allowed to grow until first flowers.  Shoot tissue was harvested, mass determined, freeze-dried, and glucosinolates analyzed.  Shoot mass at flowering ranged from 2.97 (PI263866) to 39.71 (PI597864) g/plant.  Generally, total glucosinolates levels were similar among accessions.  Ida Gold mustard (Sinapis alba, L.A. Hearne Seeds) and Red Giant mustard (Brassica juncea Integlifolia Group, Seeds of Change) had higher total glucosinolate levels than accessions such as Jupiter rapeseed (Brassica napus, Ames 6100, USDA Mustard Germplasm Repository).  Ida Gold is sold as a high-glucosinolate containing cultivator for biofumigation while Jupiter is an older European rapeseed cultivar.  Gluconapin and sinigrin are the predominant glucosinolates in most of the accessions, with Ida Gold containing the most gluconapin (271 µg g^-1 dry weight) and Red Giant containing the most sinigrin (128 µg g^-1 dry weight).   Progoitrin and glucoalysin were the other two common aliphatic glucosinolates.  Shoots of Red Giant mustard and Jupiter rapeseed contained the largest amount of the aromatic glucosinolate, gluconastrutiin.  Ida Gold, Jupiter, and Red Giant shoot mass were approximately 12 g/ plant. The biofumigant ability of mustard plants will depend not only on the amount of glucosinolates, but also on their shoot mass.